Felted inorganic fiber panel



United States Patent 3,184,372 FELTEI) INORGANIC FIBER PANEL Ronald F. Cotts, Evanston, Ill., assignor to The Celotex Corporation, a corporation of Delaware Filed Mar. 28, 1962, Ser. No. 183,093 4 Claims. (Cl. 162-445) This invention pertains to rigid, interfelted, inorganic fiber panels, and more particularly to such panels having fire retardant characteristics, and being suitable for use in a suspension system to form a ceiling.

There is present emphasis on the production and sale of rigid, inorganic fiber panels for use as acoustical materials which retard fire or flame from quickly penetrating a ceiling. In general, such fire retardant acoustical materials are in the form of panels or tiles made from mineral wool fibers or glass fibers with suitable binders for rigidity. In addition, finely pulverized clay may be added to increase the strength of the tiles when subject to intense heat.

Such tiles are currently available for installation in a suspension system which maintains the tiles in a position spaced from an overhead floor assembly. The tiles may be suspended by means of a system of concealed metal members which are inserted into kerfs in the side of the tile. An alternative suspension assembly may be a lay-in type wherein the individual tiles rest along their peripheral edges on an exposed suspension system. In either of these two types of suspension systems it is necessary that the individual tiles be sufficiently strong for manual handling so that they can be installed without chipping or breaking. Also, the tiles must be rigid enough to prevent unsightly deflection when spanning the area between spaced suspension members.

Additionally, it is imperative that the tiles remain in place during a fire so that the area above the ceiling is protected for as long a time as possible. Thus, it is necessary that the tiles do not shrink in length or width to any appreciable degree. If sufiicient shinkage occurs, there is the ever present danger that the tiles can fall out of the suspension system, and leave the area above the ceiling unprotected.

There is also a current trend toward larger tiles or panels. While acoustical panels are conventionally made in units of one, two or four square feet, even larger panels of 16 or 32 square feet are being demanded by architects and contractors. The adverse effects of deflection and shrinkage become more serious as the size of the tile or panel increases.

It is an object of the present invention to provide a rigid, inorganic fiber panel which shows surprising strength compared to presently available panels.

It is another object of the present invention to provide a rigid, inorganic fiber panel or acoustical tile having unusual strength with a minimum amount of lateral shrinkage.

It is yet another object of the present invention to provide a rigid panel which has a minimum amount of lateral shrinkage during exposure to flame or extreme heat.

Other objects and features of the novel acoustical tile of the present invention will become more apparent to those skilled in the art from a consideration of the detailed description of the present invention taken with the accompanying drawings, in which:

3,184,372 Fatented May 18, 1965 "ice The process of manufacturing such tile is well-known and comprises the formation of the tile on a modified Fourdrinier or papermaking machine by supplying to the headbox of the machine a mixture of mineral wool fibers suspended in a cooked starch solution. The Fourdrinier machine, by a felting process, forms a mat of the mineral wool fibers and the excess starch binder solution is drawn ofi by suction, usually through a vacuum box. The felted mat is then dried in an oven and subsequently fabricated by suitable sawing, kerfing and painting.

The tile of the present invention, as shown in FIG- URE 1, is an improvement over such mineral wool fiber tile, and is characterized by the addition to the basic formulation of a quantity of asbestos fibers. In FIG- URE l, a representative tile 10 comprises mineral wool fibers l2, asbestos fibers 13 and, if desired, clay particles 14, all dispersed in a starch binder. Asbestos is a form of magnesium silicate which occurs in fibrous form. One of the most common forms of asbestos is chrysotile (3MgO.2Sio .2II O) which comprises long fibers whose molecules are believed to be arranged in the form of concentric cylinders. Chrysotile fibers are mined from extensive deposits in Canada, Russia and Rhodesia, and are readily procurable. Another form of long asbestos fibers is amosite, which is available from mines in South Africa. The amosite fibers differ from the chrysotile fibers in that the molecules of the fibers are arranged in the form of straight narrow strips. The chrysotile and amosite fibers ditfer in their characteristics because of the arrangement of their respective molecules. Thus, the chrysotile fibers are generally softer, more flexible, and more absorbent than amosite fibers. However, despite these differences, the two forms of asbestos have been found advantageous in the present invention.

The characteristics of an acoustical tile made from a combination of mineral wool fibers and asbestos fibers may be further enhanced by the inclusion of an amount of pulverized non-swelling clay. The non-swelling clay found most suitable for the best combination of small shrinkage and good strengthhas been found to be kaolin clay, such as that available from the J. M. Huber Corporation and sold as Kaolex D-6. The clay is pulverized to a fineness such that the length and width of the clay platelet is in the range of 2 to 6 microns.

Additionally, a small amount of swelling clay, such as bentonite, may be added to the combination of mineral wool fibers, asbestos, and binder to impart additional strength to the tile.

GENERAL PROCEDURE FOR MAKING ACOUSTICAL TILE In the laboratory, acoustical tiles were made by using 14" x 14" TAPPI box. The TAPPI box is a container in the form of a hollow rectangular solid having a porous screen covering the bottom of the box. The box is connected to a vacuum pump for removing excess fluid from the box and forming a felted moist mass of mineral wool and binder on the screen. A mixture of mineral wool and other ingredients, including an aqueous starch binder, is poured into the box and is agitated until there is a uniform dispersion of the mixture. The specific formulation of the mixture will be discussed hereinafter. After complete dispersal, the excess water is drained from the surface of the board by the vacuum pump. To insure further removal of excess water and to compact the felted mass, a sheet of impervious material is placed over the mass, and the vacuum pump is applied for an additional period of time; in actual practice, for about 1 minute. The felted mass is then pressed to a thickness of 1 inch in a hydraulic press and dried at a temperature of about 250 F. for about 18 hours.

In plant operation, a Fourdrinier machine, which has been modified to accommodate the mineral wool and starch binder, is used in place of the TAPPI box; The

. mixture of mineral wool and aqueous binder is pumped into the head box of the machine and flows through a gate, which is adjusted to maintain a proper flow. This mixture is deposited on a moving screen. Excess water is drawn off first by gravity, and then by a vacuum pump. At this time there remains about 61% moistnre'in the mat. The mat is then dried in air for about an hour until the core reaches a temperature of about 90 F. Following this, the mat is placed in'an oven for about 8 hours and dried. conventionally, the oven is divided into four zones through which the mat is conveyed, spending about two hours in each zone. The zone temperatures are maintained as follows: Zone 1, 340 E; Zone 2, 330 .F.; Zone 3, 320 F.; and Zone 4,315" F. i

by suitable The dried tile is then further fabricated sanding, sawing, kerfing,.punching 'or drilling, and finally painted.

FORMULATION Materials: (1) Mineral wool (2) Starch (3) Parafiin l38-l40 F. melting point) (4) Clay. 7

MIXING The following procedure is suggested for mixing the ingredients for use in' the laboratory 14" x 14" TAPPI box. About 17.7 pounds of starch are dissolved by agitation in 31.5 pounds of hot water. About 688 grams of paraifin are added to 273 pounds of water at 177? F. The starch solution is then added to the paraflin and water and this latter mixture is heated at 172 F. for about 15 minutes. The viscosity of the cooked starch gel should be about 1200 centipoises. a

'On a per tile basis, the following formulation was made: 0.7 pound of kaolin clay, 1135 grams of mineral wool, and about 12 pounds of the starch gel, prepared as above.

The tiles were made by using the TAPPI box, as previously described. I

Using this formulation as a basis, various amounts of asbestos were substituted for the wool in the'manufacture of tiles having a mixture of mineral wool and asbestos. Additionally, tiles were made using various amounts of mineral wool and asbestos without clay.

The amosite'asbestos found to be preferable was grade A-10, an intermediate grade of fibers being between /2 to /1. inch in length. This asbestos is commercially available from the North American Asbestos Company' appears'to be in the range of 4 to 10% of asbestos. (FIG- URES 2 and 3.) Also, the addition of asbestos beyond about 8% does not appreciably enhance the stability of the tile against .Sminkage in length. FIGURES 4 and 5.)

. 4 Example v1 An acoustical tile was made in accordance with the foregoing laboratory method except that no claywas added to the formulation. The other ingredients were mixed in accordance with the method'set forth, and the tile was made in the laboratory TAPPI box. The tile was then dried overnight at 250, F. The acoustical tile was then tested to determine the Modulus of Rupture and its amount of shrinkage. The following table sets forth the results of the tests:

TABLE I Percent Density, Average Average Percent amosite V 7 pounds] M.O.R./ M.O.R./ shrinkage asbestos cu. ft. pounds/ density in length sq. in.

With reference to Table I, a series of 10 mineralfiber acoustical tile-s were made according to the general procedure set forth hereinbefore. The tiles, however, were made with various amounts of mineral Wool fiber and asbestos. The-density of each of the tiles is recorded and is slightly different in each tile. The Modulus of Rupture (M.O.R.) is shown in the table. Since the strength of an acoustical tile is a function of its, density, theeifect of the variations in density iseliminated by the calculation of M.O.R./density. This latter figure is plotted in FIGURE 2 as anordinate against the percentage of ashestos calculated according .to the formula gms. of wool X100 scissa in FIGURE 2.

This curve clearly shows a greater strength of tilebetween about 1% to 25% of asbestos. It should be noted that the peak strength of .the tile occurs at about 10%. The lowest strength is shown by the tile which has no as bestos. In fact, the strength of the tilew-ith 10% asbestos is about 72% greater than that of the tile with no asbestos.

TABLE II Percent Density, Average Average Percent asbestos pounds/cu. it. M.O.R./ M.O. R./ shrinkage pounds/sq. in. density in length While Table I and FIGURE 2 relate to a panel with no .clay, reference may be had to Table II which sets forth data relative to a panel incorporating about 0.7 pound of clay for 1135 grams of mineral Wool. The data'of Table II is shown in FIGURE 3, where it can .be seen that in the range of 0%19% asbestos, the strength of the board (M.O.R.) density is greater than its strength with no. asbestos. The peak strength occurs between 4 and 6% asbestos fibers.

SHRINKAGE IN LENGTH,

Even more striking than the increase in strength is the eifect of the addition of asbestos upon the shrinkage in length of the panel. As discussed, the panels are conventionally installed in a suspension system, and any excessive shrinkage in lateral dimensions because of extreme heat may cause the panel to fall out of the suspension system.

FIGURE 4 illustrates the efiect of the addition of asbestos in a tile without clay and is based upon the figures set forth in Table I. It is clearly evident that the addition of asbestos up to about 8% has an increasing effect in improving the resistance to shrinkage in length. Without asbestos, the panel shrinks about 27% in length. At about 8% addition of asbestos the shrinkage in length dropped rapidly to about 1.5% with a slight improvement for additional asbestos.

Similar but not as striking results were found for the addition of asbestos to panels in which an amount of clay was incorporated. As shown in FIGURE 5, the addition of about 4% of asbestos improves the resistance of the panel to shrinkage from about 3.4% to 1.2%. Additional asbestos has but a slight effect in improving the shrink resistance.

DIFFERENT TYPES OF ASBESTOS Both amosit-e asbestos and chrysotile asbestos were tested in panels made in accordance with the above procedure. The results were analogous in that the addition of a controlled amount of asbestos to panels with and Without clay showed a peak strength (M.O.R./density). There was a shift in the peak curve for chrysotile as compared with amosite in that the strength of the chrysotile panel was higher than that with amosite at all percentages of asbestos. However, the shape of the curve was similar and showed a remarkable increase in strength at about 8% addition of chrysotile asbestos.

In summary, a novel intenfelted fibrous panel of various types of inorganic fibers has been shown and described. Such a panel may be made by any conventional interfelting technique, such as a Fourdrinier or papermaking machine. The tile of the invention should not be considered to be similar to inorganic fibrous panels or tiles made by a molding process in which inorganic fibers and a suitable binder are mixed to form a slurry and then deposited in a mold. The shrinkage problems of the two types of tile differ in that a granulated type of wool is used in the molding process which has a different eifect under high temperature conditions.

While different embodiments of the present invention have been set [forth and described, other changes and modifications will occur to those skilled in the art, and it is intended to cover all such changes and modifications in the appended claims.

I claim:

1. An interfelted, rigid, inorganic fiber, acoustical panel consisting essentially of to 99.5% interfelted mineral wool fibers, 0.5 to 10% asbestos fibers and a starch binder, said starch binder including about 2.7% of non-swelling clay based on the combined weight of the fibers and being uniformly dispersed throughout said fibers.

2. An interfelted, rigid, inorganic fiber, acoustical panel consisting essentially of 9099.5% inter felted mineral wool fibers, 0.5 to 10% asbestos fibers and a starch binder, said starch binder including an efiective amount of pulverized non-swelling clay to prevent lateral shrinkage of said panel greater than 3%.

3. The acoustical panel of claim 2 in which the nonswelling clay is in the form of platelets having a length and width in the range of 2 to 6 microns.

4. The acoustical panel of claim 2 in which the nonswelling clay is kaolin clay.

References Cited by the Examiner V UNITED sTATEs PATENTS 1,119,103 12/14 Moeller 162-145 1,887,726 11/32 Weber 162145 2,717,830 9/55 Bjorkman 162-145 2,732,295 1/56 Hollenberg 162145 2,772,603 12/56 Waggoner 162--145 2,773,763 12/56 Scott 162-145 2,773,764 12/56 Park 162-145 3,007,841 11/61 Breiner 162 3,066,066 11/62 Keim 162-145 DONALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLK, Examiner, 

1. AN INTERFELTED, RIGID, INORGANIC FIBER, ACOUSTICAL PANEL CONSISTING ESSENTIALLY OF 90 TO 99.5% INTERFELTED MINERAL WOOL FIBERS, 0.5 TO 10% ASBESTOS FIBERS AND A STARCH BINDER, SAID STARCH BINDER INCLUDING ABOUT 27% OF NON-SWELLING CLAY BASED ON THE COMBINED WEIGHT OF THE FIBERS AND BEING UNIFORMLY DISPERSED THROUGHOUT SAID FIBERS. 